my z4 purchased with 5k miles on it; has died on me suddenly, losing power, hesitates and dies; this was "corrected". went fine for about 3 weeks then happened again 2 days ago. dealer says computer diagnostics show no problem so they are calling around the country for similar problem. One z4 owner told me of similar problem months ago while waiting for oil change, before I ever had a problem, as being common to z4. does anyone have info on similar problem and fix. thanks.